Convert downloaded YouTube videos (downloaded with youtube-dl) to audio-only, with no loss? [duplicate]

If one downloads videos from YouTube using youtube-dl, they get .mp4 files which are a ISO Media, MPEG v4 system, version 2.

Can these files be converted to audio-only, ideally with no quality loss?
The goal is to save space by throwing out the unneeded visual part.

Solution 1:

You can convert to audio only formats using youtube-dl itself, although it still downloads the video and then converts it.

To do this, use -x or --extract-audio to the command, for example:

youtube-dl -x 'http://www.youtube.com/watch?v=0iyeUcFKRv4&feature=c4-overview&list=UU1KPy3cAAj0i0RIFC_SzjMg'

Solution 2:

You can convert existing downloaded files using ffmpeg from the command-line

ffmpeg -i "input file.mp4" -acodec copy "output file.aac"

The "acodec copy" part is the bit that doesn't change the audio stream.

Solution 3:

YouTube Center is excellent user script, which works accross browsers, doesn't involve bloating your OS with ton of Youtube downloaders unless you're a strictly 320 kbps person for your audio files. Besides, you have Handbrake at your disposal which involves bit of a manual work but will do exactly what you want. :)